Earlier in the day, at least four people were killed and 39 injured after a bomb hidden inside a motorcycle detonated as a Pakistani politician's convoy passed by.
He also used the opportunity to again criticize Pakistan's powerful military, which has ruled the country directly or indirectly for most of its 71-year history, saying Pakistan now has a "state above the state".
Underscoring the security threat, were Friday's bombings that killed 69 people in the latest election related violence.
Police had earlier said that more than 1,000 people were in attendance at the rally.
Mr Raisani died at a hospital in Quetta, the capital of Baluchistan province, hours after being critically wounded.
Pakistani volunteers rush injured persons to a hospital in Quetta, Pakistan, Friday, July 13, 2018.
Durrani is standing against cricketer-turned-politician Imran Khan, whose Pakistan Tehreek-e-Insaf party (PTI) is one of the frontrunners in the July 25 vote.
Officials of the Bomb Disposal Squad (BDS) confirmed that it was a suicide blast.
The Tehrik-e-Taliban Pakistan had reportedly claimed responsibility behind the attack.
Raisani is the second electoral candidate to be killed in pre-election violence this week.
Raisani is the brother of the former Baluchistan chief minister, Aslam Raisani.
Following the series of attacks this week, activists called for Pakistani authorities to remain vigilant to protect candidates during the final days of the campaign season.
Bilour was part of the predominantly secular, ethnic Pashtun nationalist Awami National Party, which has long competed with religious parties for votes in Pakistan's volatile Pashtun lands, along the border with Afghanistan.
President Mamnoon Hussain and Prime Minister Nasirul Mulk also condemned the attack in separate statements.
Adding to the tension surrounding the upcoming poll, a suicide bomber hit an election rally of a regional party in southwestern Pakistan, killing 85 people.
In 2015, at least two people were killed and three others injured in a remote-controlled bomb attack on Durrani's convoy in the Narmikhel area of Bannu.
Local ANP leader Haroon Bilour was among the 22 killed.
Today's attack is the deadliest terror strike in Pakistan since the brazen terror assault on an Army school in Peshawar in December 2014 in which about 150 people, mostly students, were killed. The military denied the accusations, and said its assistance had been requested by Pakistan's election commission.